While trees prepare for winter, we get a great show


It’s officially autumn. Colorfest was a great success and the aspens in the high country are approaching peak color.

Fall is my favorite time of year. The nights are cold, but the days are warm and the color, well, it’s just spectacular. Where does this color come from? The answer to why trees change color and why some trees turn yellow and others red lies in chemistry.

The mixture of red, purple, orange and yellow is the result of chemical processes that take place in the trees as the seasons change from summer to winter.

During the spring and summer, the leaves serve as factories where most of the foods necessary for the tree’s growth are manufactured. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color. This extraordinary chemical absorbs from sunlight the energy that is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch. Along with the green pigment are yellow-to-orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot.

Most of the year, these colors are masked by great amounts of green coloring. But, in the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears and the yellow-to-orange colors become visible and give the leaves part of their fall splendor.

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